Distance measuring device and method for determining a distance

ABSTRACT

A distance measuring device and a method for determining a distance are provided. The method includes: illuminating an object with a sequence of the light pulses, capturing one arriving light pulse corresponding to an intensity T e,l  within a first integration gate, and outputting a signal value U 1 , capturing another arriving light pulse corresponding to the intensity T e,l  within a second integration gate, and outputting a signal value U 2 , capturing one arriving light pulse corresponding to an intensity I e,h  within the first integration gate and outputting a signal value U 3 , capturing the other arriving light pulse corresponding to the intensity I e,h  within the second integration gate and outputting a signal value U 4 , and calculating the distance between the distance measuring device and the object based on U 1 , U 2 , U 3 , and U 4 .

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of international patent application PCT/EP2015/076794, filed Nov. 17, 2015, designating the United States and claiming priority from German application 10 2014 117 097.0, filed Nov. 21, 2014, and the entire content of both applications is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a distance measuring device and a method for determining a distance with the distance measuring device.

BACKGROUND

Distances can be measured between a measuring device and an object without a physical contact between the device and the object by optical methods. In these methods, the object is illuminated by a light source of the device and the light back reflected from the object is then captured by a light detector of the device.

Distances can for example be determined by periodically modulating the light intensity which is emitted from the light source and by measuring the phase difference between the emitted light and the back reflected light arriving on the detector. However, due to the periodicity of the light intensity, this method results in an ambiguous distance measurement. Distances can be unambiguously determined by measuring the time of flight between the emission of a light pulse and the arrival of a back reflected light pulse on the detector.

Ambient light, for example sun-light, can interfere with the distance measurement and therefore result in a reduction of the precision for the distance measurement. Conventionally, a background measurement is carried out without illuminating the object with the light pulse. The background measurement leads to an irregular operation of the light source. The irregular operation is disadvantageous because it results in a reduction of the life time of the light source and in fluctuations of the parameters of the light pulses, in particular intensity, pulse width, rise times and/or fall times. These fluctuations cause a reduction of the precision for the distance measurement.

SUMMARY

It is an object of the invention to provide a distance measuring device and a method for measuring a distance with the distance measuring device, wherein the distance can be measured with a high precision.

The distance measuring device according to an aspect of the invention includes a light source configured to illuminate an object with light pulses having a duration T_(p), at least one photo element configured to capture the light pulses after being back reflected from the object, a trigger generator configured for controlling the emission of the light pulses and for activating the photo element during temporal integration gates, wherein the photo element is adapted to output a signal value U at the end of each integration gate with the signal value U being proportional to the energy of the light arriving on the photo element during its activation. The trigger generator stores a trigger scheme to control the emission of the light pulses such that a sequence of the light pulses including four consecutive light pulses consisting of two light pulses having an intensity I_(e,l) and two light pulses having an intensity T_(e,h) being higher than I_(e,l) is emitted and that the repetition rate 1/Δ_(rep) of the light pulses is constant, and to activate the photo element such that the delays between the integration gates and the emission start points in time of the four light pulses are such that the light pulses arriving on the photo element are captured such that one arriving light pulse corresponding to the intensity I_(e,l) and one arriving light pulse corresponding to the intensity I_(e,h) are captured by the photo element within first integration gates with an integration start point in time T_(1,s) and an integration end point in time T_(1,e) as well as the other arriving light pulse corresponding to the intensity T_(e,l) and the other arriving light pulse corresponding to the intensity I_(e,h) are captured by the photo element within second integration gates with an integration start point in time T_(2,s) and an integration end point in time T_(2,e), wherein the delay for the first integration gates is chosen such that either T_(1,s) or T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p) and the delay for the second integration gates is chosen such the respective light pulses are at least partially within the second integration gates, wherein T_(1,s), T_(1,e), T_(2,s), T_(2,e) are the delays from the emission start point in time and Δ_(tof) is the first point in time the arriving light pulses arrive on the photo element, and a processing unit adapted to calculate the distance between the distance measuring device and the object by using the difference of the signal values U being output at the end of the first integration gates and the difference of the signal values U being output at the end of the second integration gates. The duration T_(1,e)-T_(1,s) of the first integration gates can be equal to or can be different from the duration T_(2,e)-T_(2,s) of the second integration gates.

The method according to an aspect of the invention for determining a distance with the distance measuring device includes the steps of: a) illuminating the object with the sequence of the light pulses; b) capturing one arriving light pulse corresponding to the intensity I_(e,l) within one of the first integration gates, and outputting a signal value U₁ at the end of the first integration gate; c) capturing the other arriving light pulse corresponding to the intensity I_(e,l) within one of the second integration gates, and outputting a signal value U₂ at the end of the second integration gate; d) capturing one arriving light pulse corresponding to the intensity I_(e,h) within the other first integration gate and outputting a signal value U₃ at the end of the first integration gate; e) capturing the other arriving light pulse corresponding to the intensity I_(e,h) within the other second integration gate and outputting a signal value U₄ at the end of the second integration gate; f) calculating the distance between the distance measuring device and the object by using the difference of the signal values U₂ and U₁ and the difference of the signal values U₄ and U₃.

In order to arrange the integration gates with respect to the emission start point in time, a distance range in which the object can be located is predetermined. From the distance range T_(p), T_(1,s) and T_(1,e) can be chosen such that T_(1,s) or T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p) for all possible distances of the distance range. T_(2,s) and T_(2,e) can then be chosen such that the respective light pulses are at least partially within the second integration gates for all possible distances of the distance range.

According to an aspect of the invention, Δ_(tof) and Δ_(tof)+T_(p) are between T_(2,s) and T_(2,e). For the case that T_(1,s) is between Δ_(tof) and Δ_(tof)+T_(p), the time of flight Δ_(tof) from the emission of the light pulses to the arrival of the light pulses on the photo element is calculated by:

$\begin{matrix} {\Delta_{tof} = {T_{1,s} + {{T_{p}\left( {\frac{U_{3} - U_{1}}{U_{4} - U_{2}} - 1} \right)}.}}} & \left( {{equation}\mspace{14mu} 1} \right) \end{matrix}$

For the case that T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p), Δ_(tof) is calculated by:

$\begin{matrix} {\Delta_{tof} = {T_{1,e} - {T_{p}{\frac{U_{3} - U_{1}}{U_{4} - U_{2}}.}}}} & \left( {{equation}\mspace{14mu} 2} \right) \end{matrix}$

Also, according to the aspect of the invention, the durations of the first and second integration gates can be equal or can be different. If the durations are different, the duration T_(2,e)-T_(2,s) can be longer than the duration T_(1,e)-T_(1,s) to ensure that the complete light pulses are within the second integration gate.

Alternatively, according to another aspect of the invention, in case T_(1,s) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,s) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,e) is later than Δ_(tof)+T_(p) and T_(2,s) is different from T_(1,s), and in the case T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,e) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,s) is earlier than Δ_(tof) and T_(2,e) is different from T_(1,e).

For the case that T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p), Δ_(tof) is calculated by

$\begin{matrix} {\Delta_{tof} = {T_{1,e} - {\left( {T_{2,e} - T_{1,e}} \right){\frac{U_{2} - U_{1}}{\left( {U_{4} - U_{3}} \right) - \left( {U_{2} - U_{1}} \right)}.}}}} & \left( {{equation}\mspace{14mu} 3} \right) \end{matrix}$

For the case that T_(2,e) is between Δ_(tof) and Δ_(tof)+T_(p), Δ_(tof) is calculated by:

$\begin{matrix} {\Delta_{tof} = {T_{1,s} - T_{p} - {\left( {T_{2,s} - T_{1,s}} \right){\frac{U_{2} - U_{1}}{\left( {U_{4} - U_{3}} \right) - \left( {U_{2} - U_{1}} \right)}.}}}} & \left( {{equation}\mspace{14mu} 4} \right) \end{matrix}$

For all cases, the distance r between the distance measuring device and the object is then calculated by

r=0.5*c*Δ _(tof)  (equation 5),

wherein c is the speed of light in the medium in which the distance measurement is carried out.

With the distance measuring device and the method according to an aspect of the invention, it is possible to eliminate the influence of background light, for example sun light, without taking a background measurement. The background measurement would include outputting a signal value U at the end of an integration gate without illuminating the object with a light pulse. Since it is not necessary to take the background measurement, it is possible to operate the light source with the constant repetition rate 1/Δ_(rep), which results in a long life time of the light source. Δ_(rep) denotes the duration between two consecutive emission start points in time. Another advantage of the constant repetition rate is that the intensity fluctuations of the light pulses are reduced. Both, the elimination of the influence of the background light and the reduction of the intensity fluctuations result in a high precision for the distance measurement.

According to an aspect of the invention, the trigger scheme controls the emission of the sequence such that single light pulses having the intensity T_(e,l) are emitted alternating with single light pulses having the intensity I_(e,h). This results in a particular regular operation of the light source which results in a particular long life time of the light source and in particular small intensity fluctuations of the light pulses. According to an aspect of the invention, the trigger scheme controls the emission of the light pulses such that the sequence includes a dummy light pulse preceding the four light pulses. Since the dummy light pulse is not used for the distance measurement, it is advantageously achieved that only light pulses with small intensity fluctuations are used for the distance measurement. According to another aspect of the invention, the trigger scheme controls the emission of the light pulses such that the sequence includes a plurality of dummy light pulses, wherein at least one dummy light pulse precedes each of the four light pulses. By using the multitude of dummy light pulses, it is possible to maintain a stable and constant repetition rate 1/Δ_(rep) and to carry out the measurements of the signal values U at a measurement frequency, even if the measurement frequency of the photo element is lower than repetition rate 1/Δ_(rep) for a stable operation of the light source.

According to an aspect of the invention, the light source includes light emitting diodes, VCSELs (vertical-cavity surface-emitting laser) and lasers or any combination thereof that are in particular configured to emit in the visible and/or infrared spectral region. According to another aspect of the invention, the distance measuring device includes a CCD chip with an image intensifier and/or a CMOS chip that includes the at least one photo element.

According to a further aspect of the invention, the light source includes a first group with at least one light emitting diode, VCSEL and/or laser and a second group with at least one light emitting diode, VCSEL and/or laser, wherein the trigger scheme controls the emission of the light pulses such that the first group emits light pulses with the repetition rate 1/Δ_(rep) and with the intensity I_(e,l) and such that the second group emits light pulses with the repetition rate 0.5/Δ_(rep) and with the intensity I_(e,h)-I_(e,l) so that the overlap of the emission of the first group and second group results in the light pulses with the intensity I_(e,h). Here, it is advantageously achieved that the first group and the second group are operated perfectly regularly so that the life times of the first group and the second group are particularly increased.

According to an aspect of the invention, Δ_(tof) and Δ_(tof)+T_(p) are between T_(2,s) and T_(2,e). Alternatively, according to another aspect of the invention, in case T_(1,s) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,s) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,e) is later than Δ_(tof)+T_(p) and T_(2,s) is different from T_(1,s), and in case T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,e) is between Δ_(tof) and Δ_(tof)+T_(p), T_(2,s) is earlier than Δ_(tof) and T_(2,e) is different from T_(1,e).

According to an aspect of the invention, in step a) the sequence is such that single light pulses having the intensity I_(e,l) are emitted alternating with single light pulses having the intensity I_(e,h). The sequence preferably includes a dummy light pulse preceding the four light pulses, wherein the dummy light pulse is not used for the determination of the distance. According to an aspect of the invention, the sequence includes a plurality of dummy light pulses, wherein at least one dummy light pulse precedes each of the four light pulses, wherein the dummy light pulses are not used for the determination of the distance. According to another aspect of the invention, in step a) the sequence includes a multitude of sets of the four light pulses and a respective distance is determined for each set by repeating steps b) to f).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings wherein:

FIG. 1 shows temporal profile diagrams with integration gates and intensities of light pulses, and

FIG. 2 shows a schematic cross section through a distance measuring device.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 2 shows a distance measuring device 14 including a light source 15, a photo element 16, a trigger generator 17, a memory unit 18 and a processing unit 19. The light source 15 includes light emitting diodes, VCSEL (vertical-cavity surface-emitting laser) and/or lasers, wherein the light emitting diodes, the VCSELs and/or the lasers are configured to emit in the visible and/or infrared spectral region. The distance measuring device 14 includes a CCD chip with an image intensifier and/or a CMOS chip that includes the at least one photo element 16. The CMOS chip includes at least one condenser that can be discharged via a photodiode. The trigger generator 17 provides an activation signal 25 for controlling the emission of the light source 15 and an activation signal 26 for activating the photo element 16 during a temporal integration gate 6. The CCD chip is activated by switching on the image intensifier and the CMOS chip is activated by closing a switch in the circuit of the condenser and the photodiode, which allows that the condenser is discharged via the photodiode. The photo element 16 is configured to output a signal value U at the end of the integration gate 6, wherein the signal value U is proportional to the energy of the light arriving on the photo element during its activation. The signal value U is read out in a readout operation 27 and stored in the memory unit 18. The memory unit 18 is configured to store a multitude of signal values U. The multitude of the signal values U is then processed by the processing unit 19 in a processing operation 28 in order to determine a distance between the distance measuring device 14 and an object 22.

The signal value U can be measured directly, for example if a CCD chip or CMOS image sensor is used. The charge measured at the end of the integration gate is proportional to the energy of the light arriving on the photo element during its activation and therefore the signal value U, which is proportional to the charge, is proportional to the energy of the light. On the other hand, the signal value U can be determined indirectly if the relation between a measured value and the energy of the light arriving on the photo element during its activation is known. For example, if the photo element includes a condenser that is discharged via a photodiode during the activation of the photo element, the measured value is a voltage that is approximately inversely proportional to the energy of the light arriving on the photo element during its activation.

Detection optics 21 are arranged in front of the photo element 16 in order to image a field of view 24 onto the photo element 16. Illumination optics 20 are arranged in front of the light source 15 in order to shape the light emitted by the light source 15 such that an illumination area 23 can be illuminated by the light source 15. The illumination area 23 and the field of view 24 are shaped such that the field of view 24 is substantially completely covered by the illumination area 23. The distance measuring device 14 is adapted such that the light emitted by the light source 15 impinges onto the object 22 located within the field of view 24, and arrives on the photo element 16 after being back reflected from the object 22. The illumination optics 20 and the detection optics 21 are preferably respective lenses. It is also possible to use a single lens for both the illumination optics 20 and the detection optics 21.

In FIG. 1, three temporal profile diagrams are shown, wherein an intensity 1 and an integration gate 2 are plotted versus time 3. The first temporal profile diagram is a plot of the intensity 4 of the emitted light pulses 7, 8 versus the time 3, the second temporal profile diagram is a plot of the intensity 5 of the light pulses 9, 10 arriving on the photo element 16 after being back reflected from the object 22 versus the time 3, and the third temporal profile diagram is a plot of the integration gates 6 versus the time 3.

The first temporal profile diagram shows that the light source 15 emits a sequence of consecutive light pulses 7, 8. The light pulses 7, 8 have a preferably rectangular temporal profile so that the light source 15 switches the intensity of the light pulses 7, 8 at an emission start point in time 13 from a lower intensity to a higher intensity and after a pulse duration T_(p) from the emission start point in time 13 back to the lower intensity. The pulse duration T_(p) is preferably the same for all the light pulses 7, 8 and is in the order of picoseconds or nanoseconds. The repetition rate 1/Δ_(rep) for all the light pulses in the sequence is constant, wherein Δ_(rep) is the duration between two consecutive emission start points in time 13. The repetition rate 1/Δ_(rep) for the light pulses 7, 8 is from 1 Hz to 20 kHz.

In the following it is assumed that the lower intensity is zero. The sequence includes a set of four consecutive light pulses 7, 8, wherein two light pulses 7 of the four light pulses 7, 8 have the intensity I_(e,l) and the other two light pulses 8 the four light pulses 7, 8 have the intensity I_(e,h), wherein I_(e,h)>I_(e,l). In the sequence, a single light pulse 7 with the intensity I_(e,l) and a single light pulse 8 with the intensity I_(e,h) are always emitted alternatingly. After the emission, the light pulses 7, 8 impinge on the object 22 located within the field of view 24 and are back reflected from the object 22. Afterwards the light pulses 9, 10 arrive on the photo element 16, wherein Δ_(tof) is the first point in time from the emission start point in time 13, when the light pulses 9, 10 arrive on the photo element 16. The two light pulses 9 arriving on the photo element 16 and corresponding to the light pulses 7 with the intensity I_(e,l) have the intensity I_(a,l), wherein I_(a,l)<I_(e,l). The two light pulses 10 arriving on the photo element 16 and corresponding to the light pulses 8 with the intensity I_(e,h) have the intensity I_(a,h), wherein I_(a,h)<I_(e,h).

The third temporal profile diagram shows that the set of the four light pulses 9, 10 arriving on the photo element 16 are captured within two first integration gates 11 and two second integration gates 12. The first integration gates 11 have an integration start point in time T_(1,s) and an end integration end point in time T_(1,e), wherein T_(1,s) and T_(1,e) are the delays from the emission start point in time 13. The second integration gates 12 have an integration start point in time T_(2,s) and an integration end point in time T_(2,e), wherein T_(2,s) and T_(2,e) are the delays from the emission start point in time 13. One of the four light pulses 9 having the intensity I_(a,l) and one of the four light pulses 10 having the intensity I_(a,h) are captured by the photo element 16 within a respective first integration gate 11 such that T_(1,e) is between Δ_(tof) and Δ_(tof)+T_(p) and that T_(1,s) is earlier than Δ_(tof). Alternatively, it is possible that the respective first integration gate 11 is such that T_(1,s) is between Δ_(tof) and Δ_(tof)+T_(p) and that T_(1,e) is later than Δ_(tof)+T_(p). The other of the four light pulses 9 having the intensity I_(a,l) and the other of the four light pulses 10 having the intensity I_(a,h) are captured by the photo element 16 within a respective second integration gate 12 such that Δ_(tof) and Δ_(tof)+T_(p) are between T_(2,s) and T_(2,e).

The hatched areas in the second temporal profile diagram are proportional to the energy of the light arriving on the photo element 16 during its activation. Since the signal value U is proportional to the energy of light arriving on the photo element during its activation, the signal value U is also proportional to the hatched areas. A signal value U₁ is put out at the end of the first integration gate 11 that captures one of the light pulses 9 with the intensity I_(a,l). A signal value U₃ is output at the end of the first integration gate 11 that captures one of the light pulses 10 with the intensity I_(a,h). A signal value U₂ is put out at the end of the second integration gate 12 that captures the other of the light pulses 9 with the intensity I_(a,l). A signal value U₄ is put out at the end of the second integration gate 12 that captures the other of the light pulses 10 with the intensity I_(a,h).

FIG. 1 shows that Δ_(tof)+U₁/I_(a,l)=T_(1,e) and Δ_(tof)+U₃/I_(a,h)=T_(1,e). These two equations are equivalent to:

$\begin{matrix} {{I_{a,l} = \frac{U_{1}}{T_{1,e} - \Delta_{tof}}}{and}} & \left( {{equation}\mspace{14mu} 6} \right) \\ {I_{a,h} = {\frac{U_{3}}{T_{1,e} - \Delta_{tof}}.}} & \left( {{equation}\mspace{14mu} 7} \right) \end{matrix}$

Furthermore, FIG. 1 shows that U₂=T_(p)*I_(a,l) and U₄=T_(p)*I_(a,h). These two equations are equivalent to:

$\begin{matrix} {{I_{a,l} = \frac{U_{2}}{T_{p}}}{and}} & \left( {{equation}\mspace{14mu} 8} \right) \\ {I_{a,h} = {\frac{U_{4}}{T_{p}}.}} & \left( {{equation}\mspace{14mu} 9} \right) \end{matrix}$

By subtracting equation 6 from equation 7 and equation 8 from equation 9 it follows:

$\begin{matrix} {{{I_{a,h} - I_{a,l}} = {\frac{1}{T_{1,e} - \Delta_{tof}}\left( {U_{3} - U_{1}} \right)}}{and}} & \left( {{equation}\mspace{14mu} 10} \right) \\ {{I_{a,h} - I_{a,l}} = {\frac{1}{T_{p}}{\left( {U_{4} - U_{2}} \right).}}} & \left( {{equation}\mspace{14mu} 11} \right) \end{matrix}$

By equalizing the right hand sides of equation 10 and equation 11, it is then possible to derive equation 2. Equation 3 can be derived in an analogous manner. By subtracting the equations 6 to 9, the influence of background light is eliminated.

The sequence can include a dummy light pulse preceding the set of the four light pulses 7, 8, wherein the dummy light pulse is not used for the determination of a distance. In this case, the dummy light pulse has an emission start point in time that is a duration Δ_(rep) earlier than the emission start point in time 13 of the earliest of the four light pulses 7, 8.

The sequence can also include a multitude of dummy pulses preceding each of the four light pulses 7, 8 wherein the dummy light pulses are not used for the determination of a distance. In these cases, the dummy light pulses have emission start points in time that are earlier than the emission start point of the respective measurement light pulse 7, 8.

Furthermore, the sequence can include a multitude of the sets of the four light pulses 7, 8 and a respective distance is calculated for each of the sets. If the sequence includes the multitude of the sets, the repetition rate of all the light pulses is maintained constant with the repetition rate 1/Δ_(rep). The distance measuring device 14 can include a plurality of photo elements 16 and a respective distance is determined for each of the photo elements 16.

In an exemplary embodiment, the light source includes a first group with at least one light emitting diode, VCSEL and/or laser and a second group with at least one light emitting diode, VCSEL and/or laser, wherein the emission of the light pulses is controlled such that the first group emits light pulses with the repetition rate 1/Δ_(rep) and with the intensity I_(e,l) and such that the second group emits light pulses with the repetition rate 0.5/Δ_(rep) and with the intensity I_(e,h)-I_(e,l) so that the overlap of the emission of the first group and second group results in the light pulses with the intensity I_(e,h).

It is understood that the foregoing description is that of the exemplary embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST OF REFERENCE NUMERALS

-   1 intensity -   2 integration gate -   3 time -   4 intensity of emitted light pulses -   5 intensity of arriving light pulses -   6 integration gates -   7 emitted light pulse with low intensity -   8 emitted light pulse with high intensity -   9 arriving light pulse with low intensity -   10 arriving light pulse with high intensity -   11 first integration gate -   12 second integration gate -   13 emission start point in time -   14 distance measuring device -   15 light source -   16 photo element -   17 trigger generator -   18 memory unit -   19 processing unit -   20 illumination optics -   21 detection optics -   22 object -   23 illumination area -   24 field of view -   25 activation signal for light source -   26 activation signal for photo element -   27 readout operation -   28 processing operation -   Δ_(rep) repetition duration -   T_(p) pulse duration -   Δ_(tof) time of flight -   T_(1,s) integration start point in time of first integration gate -   T_(1,e) integration end point in time of first integration gate -   T_(2,s) integration start point in time of second integration gate -   T_(2,e) integration end point in time of second integration gate -   I_(e,l) intensity of emitted light pulse -   I_(e,h) intensity of emitted light pulse -   I_(a,l) intensity of arriving light pulse -   I_(a,h) intensity of arriving light pulse 

What is claimed is:
 1. A distance measuring device comprising: a light source configured to illuminate an object with emitted light pulses, the emitted light pulses having a pulse duration T_(p); at least one photo element configured to capture arriving light pulses after being back reflected from the object; the arriving light pulses including first arriving light pulses and second arriving light pulses; a trigger generator configured for controlling an emission of the emitted light pulses and for activating the at least one photo element during temporal integration gates; the temporal integration gates including first and second temporal integration gates; the at least one photo element being configured to output a signal value U at an end of each of the temporal integration gates, the signal value U being proportional to an energy of light arriving on the at least one photo element when the at least one photo element is activated; the trigger generator being configured to store a trigger scheme to control the emission of the emitted light pulses such that a sequence of the emitted light pulses is emitted and a repetition rate 1/Δ_(rep) of the emitted light pulses is constant; the sequence of the emitted light pulses including four consecutively emitted light pulses; the four consecutively emitted light pulses including two first emitted light pulses having a first intensity I_(e,l) and two second emitted light pulses having a second intensity I_(e,h); the second intensity I_(e,h) being higher than the first intensity I_(e,l); the trigger generator being configured to activate the at least one photo element such that delays between the temporal integration gates and emission start points in time of the four consecutively emitted light pulses are such that the arriving light pulses arriving on the photo element are captured such that one first arriving light pulse corresponding to the first intensity I_(e,l) and one second arriving light pulse corresponding to the second intensity I_(e,h) are captured by the at least one photo element within the first integration gates with a first integration start point in time T_(1,s) and a first integration end point in time T_(1,e) and another first arriving light pulse corresponding to the first intensity I_(e,l) and another second arriving light pulse corresponding to the second intensity I_(e,h) are captured by the at least one photo element within the second integration gates with a second integration start point in time T_(2,s) and a second integration end point in time T_(2,e); a delay for the first integration gates being selected such that either the first integration start point in time T_(1,s) or the first integration end point in time T_(1,e) is between a time of flight Δ_(tof) and a sum of the time of flight and the pulse duration Δ_(tof)+T_(p); a delay for the second integration gates being selected such that respective arriving light pulses are at least partially within the second integrations gates; the first integration start point in time T_(1,s), the first integration end point in time T_(1,e), the second integration start point in time T_(2,s), and the second integration end point in time T_(2,e) being the delays from the emission start points in time and Δ_(tof) being a first point in time the arriving light pulses arrive on the at least one photo element, and a processing unit configured to calculate a distance between the distance measuring device and the object based on a difference of signal values U being outputted at the end of the first integration gates and the difference of the signal values U being outputted at the end of the second integration gates.
 2. The distance measuring device of claim 1, wherein the trigger scheme controls the emission of the sequence of the emitted light pulses such that the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p) are between the second integration start point in time T_(2,s) and the second integration end point in time T_(2,e).
 3. The distance measuring device of claim 1, wherein the trigger scheme controls the emission of the sequence of the emitted light pulses such that: when the first integration start point in time T_(1,s) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration start point in time T_(2,s) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration end point in time T_(2,e) is later than the sum of the time of flight and the pulse duration Δ_(tof)+T_(p) and the second integration start point in time T_(2,s) is different from the first integration start point in time T_(1,s), and when the first integration end point in time T_(1,e) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration end point in time T_(2,e) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration start point in time T_(2,s) is earlier than the pulse duration Δ_(tof) and the second integration end point in time T_(2,e) is different from the first integration end point in time T_(1,e).
 4. The distance measuring device of claim 1, wherein the trigger scheme controls the emission of the sequence of the emitted light pulses such that single first light pulses having the first intensity I_(e,l) are emitted alternating with single second light pulses having the second intensity I_(e,h).
 5. The distance measuring device of claim 1, wherein: the trigger scheme controls the emission of the light pulses such that the sequence includes a dummy light pulse preceding the four consecutively emitted light pulses or such that the sequence includes a plurality of dummy light pulses, and at least one dummy light pulse precedes each of the four consecutively emitted light pulses.
 6. The distance measuring device of claim 1, wherein the light source includes at least one of light emitting diodes, VCSELs and lasers that are configured to emit light in at least one of a visible spectral region and an infrared spectral region.
 7. The distance measuring device of claim 1, wherein: the light source includes a first group with at least one of a light emitting diode, a VCSEL and a laser, and a second group with at least one of the light emitting diode, the VCSEL, and the laser, the trigger scheme controls the emission of the light pulses such that: the first group emits the light pulses with the repetition rate 1/Δ_(rep) and with the first intensity I_(e,l), and the second group emits the light pulses with a repetition rate 0.5/Δ_(rep) and with an intensity I_(e,h)-I_(e,l) such that an overlap of the emission of the light pulses of the first group and second group results in the light pulses with the second intensity I_(e,h).
 8. The distance measuring device of claim 1, further comprising at least one of a CCD chip with an image intensifier, and a CMOS chip that includes the at least one photo element.
 9. A method for determining a distance by the distance measuring device of claim 1, the method comprising the steps of: a) illuminating the object with the sequence of the emitted light pulses; b) capturing one arriving light pulse corresponding to the first intensity T_(e,l) within one of the first integration gates, and outputting a first signal value U₁ at an end of the one of the first integration gates; c) capturing another arriving light pulse corresponding to the first intensity T_(e,l) within one of the second integration gates, and outputting a second signal value U₂ at an end of the one of the second integration gates; d) capturing one arriving light pulse corresponding to the second intensity I_(e,l) within another one of the first integration gates and outputting a third signal value U₃ at an end of the other one of first integration gates; e) capturing another arriving light pulse corresponding to the second intensity I_(e,h) within the another one of the second integration gates and outputting a fourth signal value U₄ at an end of the other one of the second integration gates; f) calculating the distance between the distance measuring device and the object based on a difference between the second signal value U₂ and the first signal value U₁ and a difference between the fourth signal value U₄ and the third signal value U₃.
 10. The method of claim 9, wherein the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p) are between the second integration start point in time T_(2,s) and the second integration end point in time T_(2,e).
 11. The method of claim 9, wherein: when the first integration start point in time T_(1,s) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration start point in time T_(2,s) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration end point in time T_(2,e) is later than the sum of the time of flight and the pulse duration Δ_(tof)+T_(p) and the second integration start point in time T_(2,s) is different from the first integration start point in time T_(1,s), and when the first integration end point in time T_(1,e) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration end point in time T_(2,e) is between the time of flight Δ_(tof) and the sum of the time of flight and the pulse duration Δ_(tof)+T_(p), the second integration start point in time T_(2,s) is earlier than the time of flight Δ_(tof) and the second integration end point in time T_(2,e) is different from the first integration end point in time T_(1,e).
 12. The method of claim 9, wherein in step a) the sequence of the emitted light pulses is such that single light pulses having the first intensity T_(e,l) are emitted alternating with single light pulses having the second intensity I_(e,h).
 13. The method of claim 9, wherein: the sequence of the emitted light pulses includes a dummy light pulse preceding the four consecutively emitted light pulses or a plurality of dummy light pulses, at least one dummy light pulse precedes each of the four consecutively emitted light pulses, and none of the dummy light pulses is used for the determination of the distance.
 14. The method of claim 9, wherein in step a) the sequence of the emitted light pulses includes a plurality of sets of the four consecutively emitted light pulses and a respective distance is determined for each set by repeating steps b) to f).
 15. The method of claim 9, wherein: the light source includes a first group with at least one of a light emitting diode, a VCSEL and a laser, and a second group with at least one of the light emitting diode, the VCSEL, and the laser, the emission of the light pulses is controlled such that: the first group emits the light pulses with a repetition rate 1/Δ_(rep) and with the first intensity I_(e,l), and the second group emits the light pulses with a repetition rate 0.5/Δ_(rep) and with an intensity I_(e,h)-I_(e,l) such that an overlap of the emission of the light pulses of the first group and second group results in the light pulses with the second intensity I_(e,h). 